Many procedures for manufacturing flexible polymeric containers such as plastic bags include the process of forming a continuous tubular enclosure by folding a traveling web of polymer film material upon itself and sealing the juxtaposed edges together. The sealing step may be accomplished by heat sealing or by use of an adhesive. The adhesive sealing procedure includes the step of applying a continuous strip of adhesive to the traveling web as a narrow coating. This strip of adhesive is laid onto the web as a viscous liquid film that is transferred from an anilox roll for example in rolling contact with the traveling web.
Some of the more effective adhesive compositions necessarily include volatile, combustible solvents. After the adhesive is coated onto the web at the desired location, the solvent is removed from the coated strip by evaporation leaving the stable adhesive solids. Subsequently, the web is slit, turned upon itself and the edges laid together. The strip of adhesive is heated under compressive pressure to activate the adhesive and seal the edges together.
Volatile, combustible solvents frequently constitute a health hazard as well as a safety hazard in the industrial environment. Accordingly, it is essential to users of these materials to keep the generally occupied plant environment substantially free of fugitive vapors. To this end, web processing machines using these materials are usually covered by ventilation hoods or more comprehensive enclosures that discharge environmental air drawn from around the machine into a vapor recovery system. Even so, vapor recovery is an expensive overhead cost to the manufacturing process. Given the value of the process, it would be considerably less expensive to restrict the release of such vapors than to recover them after release. However, the manufacturing process requires a continuously traveling web which frustrates many efforts to limit release of harmful solvent vapors.
An example of difficulties encountered by vapor control efforts arises from the prior art process by which an adhesive strip is coated onto the polymer web. This prior art process includes an anilox roll that extends the full width or cross direction of the production machine. Such width may be five to ten feet, for example. The polymer web width carried in a typical bag machine, for example, may represent several tubes, each of which is to receive, for example, a 1/2 inch wide coating of adhesive along the length of the web. For example, if 5 tubes are to be formed from an 8 ft. wide web, the total width of adhesive coating applied to the web is only 21/2 in. In order to apply 5, 1/2 in. wide continuous strips of adhesive to the web, an 8 ft. long (machine width) anilox roll rotating in an 8 ft. long open pan of the solvent diluted adhesive is used. Much of the adhesive picked up by the anilox roll surface is immediately doctored from the roll surface except for the selectively positioned 1/2 in. bands of adhesive. Unless the entire roll and pan are covered and connected to a vapor recovery system, the open atmosphere exposure of the adhesive pond in the pan may release a large amount of solvent vapors to the surrounding environment.
It is important to understand that the exact position, number and width of the adhesive strips may frequently change depending on the specification and quantity of product being manufactured on a particular day or hour. Hence, although the entire 8 ft. length of the anilox roll may be used to apply adhesive over an extended time frame, only a few inches of the roll length may be used at any given moment.
It is therefore, an object of the present invention to reduce the quantity of fugitive vapor released by web processing environment.
Another object of the present invention is to secure greater control over the release of fugitive solvent vapors from a web processing machine.
Also an object of the present invention is to provide an adhesive application apparatus having minimal solvent release.
A further object of the invention is to provide an improved adhesive coating strip application apparatus.
It is also an object of the present invention to capture and confine fugitive vapors from an anilox transfer roll at the point of release.
Another object of the invention is to provide a cost effective process for disposing of fugitive solvent vapor.
A still further object of the invention is to provide a system for recovering energy values from fugitive solvent vapor emitted from a continuous web coating process.